Adding option to save and load state by timestamp

Load by timestamp: load last state is expanded from 1 to 8 actions, for newest to oldest state

Save by timestamp: overwrite the oldest state (or use an empty slot if available). This wait for a save to be written (before allowing another state to be saved) because it must reliably know which files are on disk

Adding remaining hardcoded state keys to hotkey dialog

Adding a program exit hotkey
Changing state time data from file system mtime to a state timestamp because that allow sub-second time difference between states which can be created if the storage media is fast